Yokogawa Button Operated MV2000 - Manual (Page 66)

3-7
IM MV1000-17E
Using the Serial Interface
1
2
3
4
5
6
7
App
Index
Note
• The way to eliminate noise varies depending on the situation. In the connection example, the
cable shield is connected only to the MV’s ground (one-sided grounding). This is effective
when there is a difference in the electric potential between the PC’s ground and the MV’s
ground, which may be the case with long distance communications. If there is no difference
in the electric potential between the PC’s ground and the MV’s ground, connecting the cable
shield to ground at both ends may be effective (two-sided grounding). In some cases, using
two-sided grounding with a capacitor connected in series at one end is effective. Consider
these possibilities to eliminate noise.
• When using the two-wire system (Modbus protocol), the 485 driver must be set to high
impedance within 3.5 characters after the last data byte that the host PC sends.
Serial Interface Converter
We recommend the following converter.
MODEL RC-770X by SYSMEX RA CO.,LTD; SI-30FA by LINE EYE; or ML2 by
YOKOGAWA.
CAUTION
In converters other than those that we recommend, the FG and SG terminals may
not be isolated. In such case, do not follow the diagram on the previous page (do
not connect anything to the FG and SG terminals). Especially in long distance
communications, the potential difference that occurs may damage the instruments
or may cause communication errors. For converters that do not have the SG
terminal, they can be used without the signal ground. For details, see the converter
manual.
In converters other than those that we recommend, the signal polarities may be reversed
(A/B or +/- indication). In this case, reverse the connection.
In the case of a two-wire system, the host device must control the converter transmission
driver to prevent collisions of transmitted and received data. If you are using one of the
recommended converters, control the transmission driver using the RS (RTS) signal on
the RS-232.
When the System Contains Instruments That Only Support the RS-422
Interface
In a four-wire system, up to 32 MVs can connect to a single host device. However, this
may not be possible if the system contains instruments that support only the RS-422
interface.
When the System Contains YOKOGAWA Recorders That Only Support the
RS-422 Interface
Only up to 16 instruments can be connected. Some of the conventional YOKOGAWA
recorders (HR2400 and μR, for example) only support the RS-422 driver. If the system
contains these recorders, only up to 16 instruments can be connected.
Note
In the RS-422 standard, the maximum number of connections that are allowed on one port is
10 (for a four-wire system).
Terminator
In a multidrop connection (including point-to-point connection), connect a terminator to
the MV if the MV is connected to the end of the chain. Do not connect a terminator to a
MV in the middle of the chain. In addition, turn the host device terminator ON (see the
host device manual). If a converter is being used, turn ON its terminator. We recommend
converters with a built-in terminator.
Select the appropriate terminator (120 Ω), indicated in the figure, according to the
characteristic impedance of the line, the installation conditions of the instruments, and so
on.
3.2 Connecting the MV